Electrodeposition of a rhodium-indium alloy



United States Patent 3,311,547 ELECTRODEPQSETIGN 0F A RHODIUM-HNDIUM ALLOY Reginald Robert Benham, Letchworth, England, assignor to Johnson Matthey 8: Company Limited, London, England, a British company No Drawing. Filed Feb. 25, 1964, Ser. No. 347,119 17 Claims. (Cl. 204-43) This invention relates to improvements in and relating to the electrodeposition of rhodium.

Electrodeposited rhodium has found considerable favor in recent years both as a decorative coating material and as a contact face material owing to its extreme hardness and its resistance to corrosion and tarnish, being unaffected by attack by all acids and chemicals under normal conditions.

Rhodium is usually deposited from an electrolyte comprising an aqueous solution of rhodium sulphate or phosphate, but the use of an aqueous rhodium perchlorate solution has also been suggested. Deposits of rhodium obtained with the use of the above electrolytes exhibit the desirable characteristics of permanence and resistance to corrosion and to wear, having a hardness of the order of 800 V.P.N. coupled with exceptionally high resistance to heat and good electrical conductivity, which render them particularly suitable for use not only as protective coatings for silver ware, silver electroplate and silver jewelry, but also for protecting parts of radio, electronic or other apparatus, particularly where good contact is required. It has been found, however, that, particularly in the case of relatively thick deposits, such as are usually required for electrical contact purposes, the deposit is liable to be brittle.

The applicant has investigated this problem and has found that this tendency to brittleness of pure rhodium deposits can be overcome, without affecting the advantageous characteristics of the deposit, if there is co-deposited with the rhodium a small amount of another selected metal.

The principal object of this invention, therefore, is to overcome the disadvantages, hitherto associated with the electrodeposition of rhodium, and to provide an improved method of, and an electrolyte for use in, obtaining a predominantly rhodium electrodeposit which exhibits little or no tendency to crack, even when deposited as a relatively thick layer.

Another object of the invention is to enable a predominantly rhodium-containingalloy electrodeposit to be obtained which shall exhibit the inherently advantageous characteristics associated with pure rhodium deposits, without the tendency to brittleness of such deposits.

With these and other objects in view, the invention provides a plating bath or electrolyte for the electrodeposition of rhodium in the form of a predominantly rhodiumcontaining non-brittle alloy deposit comprising an aqueous solution of a suitable rhodium salt to which is added a minor amount of an indium salt which is compatible with said rhodium salt.

In carrying out the invention in practice, I have found that satisfactory results may be obtained by the addition to a normal rhodium plating solution of from 0.01 to 1.0 gram/liter of solution of indium in the form of a compatible indium salt. A suitable current density is from 2.5 to 20 amps/sq. ft.

The indium is preferably present in the electrolyte in the form of the same salt as that in which the rhodium is present in the solution. For example, indium sulphate is preferably used with a rhodium sulphate electrolyte or indium perchlorate with a rhodium perchlorate electrolyte. It is to be understood, however, that this is not "ice a necessary requirement, but that other salts of indium which are compatible with the other constituents of the electrolyte may be used.

The invention also provides a method of depositing on a basis material a hard non-brittle layer consisting predominantly of rhodium which method comprises co-depositing on said basis material an alloy of rhodium with indium from a plating bath or electrolyte comprising an aqueous solution of a suitable salt of rhodium and a minor amount of a salt of indium, which is compatible with said rhodium salt.

The amount of the alloying metal co-deposited with the rhodium will depend on the amount of the metal initially in the electrolyte and on the current density employed during the plating operation. With a solution containing a selected amount of the alloying metal, the amount of the metal co-deposited will be greater and higher the current density employed. This is clearly shown in the following examples indicating the percentage of in dium in a rhodium-indium alloy deposited from various electrolytes in accordance with the invention and operated at different current densities.

Example I Rhodium (as sulphate) gms./liters 812 Indium (as sulphate or other compatible salt) do 0.1 Water to 1 liter. Current density amperes/sq. ft 5 Indium content of deposit percent 0.l Rate of deposition inch per hour 0.00017 Example 11 Rhodium (as sulphate) gms./liters 8-12 Indium (as sulphate or other compatible salt) do 0.1 Water to 1 liter. Current density amperes/sq. ft 10 Indium content of deposit percentu 0.12 Rate of deposition inch per hour 0.00015 Example III Rhodium (as sulphate) gms./liters 8-12 Indium (as sulphate or other compatible salt) do- 0.5 Water to =1 liter. Current density amperes/sq. ft 5 Indium content of deposit percent 0.25 Rate of deposition inch per hour 0.000217 Example IV Rhodium (as sulphate) -gms./liters 8-12 Indium (as sulphate or other compatible salt) do 0.5 Water to 1 liter. Current density amperes/sq. ft. 10 Indium content of deposit "percent" 0.8 Rate of deposition inch per hour 0.00015 Example V Rhodium (as perchlorate) gms./-liters 8-12 Indium (as perchlorate or other compatible salt) do 0.1 Water to 1 liter. Current density amperes/sq. ft.-- 5 Indium content of deposit percent 0 .1 Rate of deposition tlIICh per hour 0.00016 3 Example VI Rhodium (as perchlorate) gms./liters 8-12 Indium (as perchlorate or other compatible salt) do 0.1 Water to 1 liter. Current density amperes/sq. ft.-- 10 Indium content of deposit percent 0.22 Rate of deposition inch per hour v 0.00017 In practice it will be found that the current density may be varied from 2.5 to amps/sq. ft.

The plating conditions are preferably so controlled that the alloy deposit obtained contains from 0.1 to 1% of indium.

The rhodium-indium alloy deposit will be found to be considerably less brittle than a pure rhodium deposit of similar thickness, but will be slightly less hard.

In general, it will be found that alloy deposits obtained in accordance with the teachings of the invention will possess all the characteristics normally associated with pure rhodium deposits, apart from a slight decrease in hardness, whilst at the same time, the tendency to brittleness, associated with normal rhodium deposits, is substantially, if not entirely, eliminated.

The invention may be used for the electroplating of any metal which may be plated with rhodium; for example, brass, bronze, copper, silver, nickel and nickel alloys may be plated direct in accordance with the teachings of the invention, and, as with pure rhodium deposits, a strike of silver may first be applied if a bright highly polished surface be required.

It is to be understood that the invention is intended to include within its scope any basis material when carrying an electrodeposited rhodium-indium alloy layer obtained by the method of, or with the use of an electrolyte in accordance with, the invention.

What I claim is:

1. An aqueous plating electrolyte for the electrodeposition of a non-brittle predominately rhodium containing alloy, said electrolyte consisting essentially of from 8 to 12 g./l. of rhodium in the form of a water soluble compound thereof and from 0.01 to 1.0 g./l. of indium in the form of a water soluble compound thereof that is compatible with said rhodium compound.

2. A plating bath as defined in claim 1 in which said indium compound and said rhodium compound are salts of the same acid.

3. A plating bath as defined in claim 1 in which said rhodium compound is rhodium sulfate.

4. A plating bath as defined in claim 1 in which said rhodium compound is rhodium perchlorate.

5. A plating bath as defined in claim 1 in which said rhodium and indium compounds are perchlorates.

6. A method which comprises electrodepositing a nonbrittle layer of a predominately rhodium-containing alloy upon a basis material from an aqueous electrolyte consisting essentially of from 8 to 12 g./l. of rhodium in the form of a water soluble compound thereof and from 0.01 to'1.0 g./l. of indium in the form of a water soluble com pound thereof that is compatible with said rhodium compound at a current density of from 2.5 to 20 amps/sq. ft.

7. A method as defined in claim 6 in which said rhodium compound is rhodium sulfate.

8. A method as defined in claim 6 in which said rhodium compound is rhodium perchlorate.

9. A method according to claim 7 in which said indium compound is indium sulphate.

10. A method according to claim 8 in which said indium compound is indium perchlorate,

11. A plating electrolyte for the electrodeposition of a non-brittle predominantly rhodium-containing alloy, said electrolyte having the following composition:

Rhodium (as sulphate) gms./liters 8-12 Indium (as sulphate) do 0.1 Water to 1.0 liter.

12. A plating electrolyte for the electrodeposition of a non-brittle predominantly rhodium-containing alloy, said electrolyte having the following composition:

Rhodium (as sulphate) gms./liters 8-l2 Indium (as sulphate) do 0.5 Water to 1.0 liter.

13. A plating electrolyte for the electrodeposition of a non-brittle predominantly rhodium-containing alloy, said electrolyte having the following composition:

Rhodium (as perchlorate) grns./liters 8-12 Indium (as perchlorate) do 0.1 Water to 1.0 liter.

14. A method of electrodepositing on a basis material a non-brittle layer of a predominantly rhodium-containing alloy which comprises depositing on said basis material a rhodium-indium alloy by electrolysing a plating electrolyte having the following composition:

Rhodium (as sulphate) gms./liters 8l2 Indium (as sulphate) do 0.1 Water to 1.0 liter. at a current density of from 2.5 to 20 amps/sq. ft.

.15. A method of electrodepositing on a basis material a non-brittle layer of a predominantly rhodium-containing alloy which comprises depositing on said basis material a rhodium-indium alloy by electrolysing a plating electrolyte having the following composition:

Rhodium (as sulphate) gms./liters 8-12 Indium (as sulphate) do 0.5 Water to 1.0 liter. at a current density of from 2.5 to 20 amps/sq. ft.

16. A method of electrodepositing on a basis material a non-brittle layer of a predominantly rhodium-containing alloy which comprises depositing on said basis material a rhodium-indium alloy by electrolysing a plating electrolyte having the following composition:

Rhodium (as perchlorate) gms./liters 8-12 Indium (as perchlorate) do 0.5 Water to 1.0 liter.

at a current density of from 2.5 to 20 amps/sq. ft.

References Cited by the Examiner UNITED STATES PATENTS 2,451,340 10/1948 Iernstedt 20443 2,458,839 1/1949 Dyer et al. 204-43 X 2,461,933 2/ 1949 Smith et al 204--43 X JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

6. A METHOD WHICH COMPRISES ELECTRODEPOSITING A NONBRITTLE LAYER OF A PREDOMINATELY RHODIUM-CONTINING ALLOY UPON A BAIS MATERIAL FROM AN AQUEOUS ELECTROLYTE CONSISTING ESSENTIALLY OF FROM 8 TO 12 G./1. OF RHODIUM IN THE FORM OF A WATER SOLUBLE COMPOUND THEREOF AND FROM 0.01 TO 1.0 G./1. OF INDIUM IN THE FORM OF A WATER SOLUBLE COMPOUND THEREOF THAT IS COMPATIBLE WITH SAID RHODIUM COMPOUND AT A CURRENT DENSITY OF FROM 2.5 TO 20 AMPS./SQ. FT. 